1. Field of the Invention
The present invention relates to a linkage system used, for example, for a joint of an articulated robot that performs complex processing or handling of goods in a three-dimensional space at high speed and with high precision.
2. Description of the Related Art
For example, Japanese Patent Laid-Open Publication No. 2000-94245 discloses a linkage system with a parallel link mechanism that performs complex processing or handling of goods in a three-dimensional space at high speed and with high precision.
The parallel link mechanism adopted in such a linkage system includes a plurality of links that connect a base plate and a traveling plate and cooperatively extend and retract to change the position and orientation of the traveling plate relative to the base plate. Tool is attached to the traveling plate of the parallel link mechanism, while a workpiece is held on a table which is designed rotatable so that the tool can freely change its position and orientation relative to the workpiece on the table and perform complex processing or handling of goods by the tool on a three-dimensional basis.
Characteristic features of such a parallel link mechanism are that the weight of the movable parts can be reduced, and positioning errors of several links are evened-out at the distal ends, both of which are advantageous for the complex, high-speed, and high-precision processing or handling of goods in the three-dimensional space.
On the other hand, if the operating range of the traveling plate needs to be increased in the parallel link mechanism, the links have to be extended because each link has a relatively small operating angle range, and the entire mechanism and then the system itself become bulky. Further, because of relatively low rigidity of the entire mechanism, the weight of the tool, or the load capacity of the traveling plate, has to be limited to a small range.
To solve the problems, the applicant of the present invention has filed a patent application relating to a linkage system with compact link mechanisms having high rigidity and large load capacity (Japanese Patent Application No. 2003-40086).
The linkage system includes three or more link mechanisms. Each link mechanism consists of end links rotatably coupled to link hubs of input and output members, respectively, and a center link to which the end links are rotatably coupled, and is geometrically identical with respect to the center cross-sectional plane on the input and output sides. Each link mechanism forms a three-link chain with four revolute joints.
In this linkage system, bearing structure is built in the link hubs, wherein outer rings of the bearing are embedded in the link hubs while inner rings of the bearing are coupled to the end links. Rotary transmission components are disposed in the space left in the link mechanisms, where drive mechanisms such as actuators are also placed for position control of the end links through the rotary transmission components, so that the output-side link hub is moved with two degrees of freedom, by driving the rotary transmission components, relative to the stationary input-side link hub.
While the linkage system is obviously operated by controlling the rotation angles of the end links, the previous patent application did not show any specific control method, nor the methods of how to determine the orientation of the output-side link hub from input rotation angles of the input-side link hub, or how to determine the rotation angles of the input-side link hubs from input data regarding the orientation of the output-side link hub.
Consequently, the present applicant has filed another patent application (Japanese Patent Application No. 2003-287945) based on the previous application (Japanese Patent Application No. 2003-40086), relating to a linkage system in which the methods of determining the orientation of the output-side link hub from input rotation angles of the input-side link hub or the rotation angles of the input-side link hubs from input data regarding the orientation of the output-side link hub.
However, there is still scope of improvement in the link mechanisms shown in these patent applications. For example, the rigidity of the link mechanism is not satisfactorily high because of cantilevered structure at the revolute joints thereof. The assemblability of the link mechanism is poor because the input-side and output-side link hubs, end links, and center links are coupled to each other with revolute joints. Furthermore, because these parts each have a complex shape, they do not lend themselves to be readily produced.
In the linkage system, the rotary transmission components are disposed in the space left in the link mechanism and the actuators for position control of the end links are provided through the rotary transmission components. Another problem was that there was little freedom of installation of the rotary transmission components and actuators because the space left in the link mechanism was small. It was hard to install other necessary parts that were large, such as rotation angle sensing means for measuring rotational angles of the input-side end links.